Once a manager or owner ASKS bout it, and Once it is known, that people are carrying, One suddenly steps across the line. Now the Company needs a written policy, and assumes certain risks and responsibilities with knowing employees are carrying, either with or without permission. Suddenly, does he need liability insurance? What about if an employee shoots someone A. in self-defences, B. Defense of others, C. Defence of property, D. Negligently, or E. by Accident? Gotten a legal opinion from both his own insurance, attorney, or the State Atty Gen'l?
It becomes a snarled tangle, especially when there is so much variance between quality of experience or training, or attitude (Rights aside, half the people I know I would NEVER go anywhere with them, if I knew they were carrying. (Nice people wrong background, experience attitude or ability)
It would probably be better if he and you just agreed that that conversation never occurred, or go through all the rigamarole, or post a notice on the door, and in the employee break room and a stuffer in their pay envelope, that carry concealed or otherwise on premises is prohibited.
On private property that is open to the public, it is all based on how much you as an owner want to risk, and assume in the way or responsibility or liability.
Attorneys will NOT give you a direct answer, they will hem and haw all around the question.